In the prior art systems for producing chorus effects from musical tone signals, the method generally followed is one in which the musical tone signal input is time delay modulated by means of a plurality of sinusoidal modulating signals having uniform phase differences to produce musical tone signals continuously varying in the frequency upwards and downwards from the frequency of the original tone signals, and mixing the original and modulated tone signals together.
However, because the time delay modulated musical tone signals, even with a low modulation frequency of 0.2-1 c/s are influenced by a vibrato effect and the phase difference between the modulated signals, is uniform, a substantial chorus effect may be heard but the feeling of vibrato is not completely cancelled, so that an adequate chorus effect is not achieved.